#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <set>
#include <map>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;

int N;
string s;
string ans;

void dfs(int a, int b, bool used, string const& str) {

  if( (N+used) % 2 == 0 && a - 1 == b ) {
    string t = str; reverse(t.begin(), t.end());
    string u = !used ? "x" : "";
    ans = str + u + t;
    return;
  }
  if( (N+used) % 2 == 1 && a - 2 == b ) {
    string t = str; reverse(t.begin(), t.end());
    string u = !used ? "x" : "";
    ans = str + u + t.substr(1);
    return;
  }

  if(s[a] == s[b]) {
    dfs(a+1, b-1, used, str + s[a]);
  }
  else if(!used) {
    dfs(a+1, b, true, str + s[a]);
    dfs(a, b-1, true, str + s[b]);
  }

}

int main() {

  cin >> s;
  N = s.size();
  dfs(0, N-1, false, "");
  if(ans.empty()) {
    cout << "NA\n";
  }
  else {
    cout << ans << endl;
  }

  return 0;
}